Nowadays, various data are involved in people's life. For example, data processing and data sharing occurs in online shopping, electronic money transfers, and electronic chatting. The safety of people's lives and property rely on reliable data security.
In an effort to prevent brute force login attempts by an automated computer program, the CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) security test has been developed. A CAPTCHA security test is used to determine whether a human or a machine is entering authentication information, thereby improving authentication security. CAPTCHAs require a manual input of data, which in turn may improve data security by a particular degree, but at the same time make operations of users increasingly complex. As a result, processing efficiency of authentication is reduced. Moreover, a conventional CAPTCHA usually includes a small character image and an entry box. Therefore, an illegal intruder may directly pull an image of a CAPTCHA very easily by using a technical solution, and then perform cracking by using an automaton. Therefore, a CAPTCHA schema still has particular vulnerabilities.